Remove the "Enable Rich Notifications" flag on ChromeOS.

ui/message_center/message_center_util.cc

Index: ui/message_center/message_center_util.cc
diff --git a/ui/message_center/message_center_util.cc b/ui/message_center/message_center_util.cc
index ba5027c0c51ee51b54ee4d5999925bd3d70c5a7b..c1dc58c3c8aafa0d10829ba93efceabd0a8c4829 100644
--- a/ui/message_center/message_center_util.cc
+++ b/ui/message_center/message_center_util.cc
@@ -13,7 +13,9 @@ namespace message_center {
 // when a time period in Canary indicates the new notifications are acceptable
 // for default behavior.
 bool IsRichNotificationEnabled() {
-#if !defined(OS_WIN) && !defined(OS_MACOSX) && !defined(USE_AURA)
+#if defined(OS_CHROMEOS)
+  return true;
+#elif !defined(OS_WIN) && !defined(OS_MACOSX) && !defined(USE_AURA)
   return false;
 #endif